The invention described herein may be manufactured, used and licensed by or for the Government for Governmental purposes without the payment to us of any royalty thereon.
1. Field of the Invention
The present invention generally relates to a comparator for use in interpreting data provided by a time-temperature indicator.
2. Problem to be Solved
Time-temperature indicators (xe2x80x9cTTIsxe2x80x9d) are used for external monitoring of the time-temperature history of various products such as food. Typically, This are used to monitor the condition of military-type rations. One such ration is typically referred to as Meal-Ready-To-Eat (xe2x80x9cMRExe2x80x9d). The quality of MRE rations is highly dependent upon the time the MREs spend in storage and the storage temperature.
There are many styles and configurations of TTIs. TTIs are generally described in the periodical entitled Food Technology, October 1991, pages 72-75. TTIs are also generally described in U.S. Pat. Nos. 5,045,283 and 5,057,434. One type of TTI is referred to as the xe2x80x9cbull""s eyexe2x80x9d style TTI and is configured as a label. The label has an adhesive backing that is adhered to a ration container. The label has a circular-shaped, outer reference portion and a circular-shaped, active portion within the reference portion. The reference and active portions are concentrically arranged. In another type of xe2x80x9cbull""s eyexe2x80x9d style TTI, the reference portion is within the active portion.
The active portion of the xe2x80x9cbull""s eyexe2x80x9d style TTI changes color over time wherein the rate of change is dependent upon the temperature to which the TTI is exposed. Specifically, the rate of darkening of the active portion is dependent upon the storage temperature. Since the quality of the MREs is highly dependent upon the time spent in storage and the storage temperature, the darkening of the active portion can be related to the expiration of the shelf life of the MREs, i.e. degradation in quality of the MREs. The xe2x80x9cbull""s eyexe2x80x9d type TTIs can be configured to have a predetermined target shelf life. Initially, the color of the active portion matches the color of the peripheral or base portion. The target shelf life is attained when the color of the active portion matches the color of the reference portion. One commercially available xe2x80x9cbull""s eyexe2x80x9d type TTIs is based on a target shelf life of three (3) years at 80xc2x0 F. Thus, if the xe2x80x9cbull""s eyexe2x80x9d type TTI is applied to rations that are stored at a temperature of 80xc2x0 F., the time it takes for the color of the active portion to match the color of the reference portion will be about three (3) years. However, if the storage temperature is greater than 80xc2x0 F., the time it takes for the color of the active portion to match the color of the reference portion will be less than three (3) years. Therefore, the quality of the MRE will be comparable to that of a MRE that was in storage for three (3) years even though it was actually in storage less than three (3) years. On the other hand, storing the rations at temperatures below 80xc2x0 F. increases the time required for the color of the active portion of the TTI to match the color of the reference portion. Thus, the shelf life of the ration is extended beyond three years.
Typically, instrumentation is used to evaluate the change in color of the active portion of the TTI in order to accurately determine the time-temperature condition of the ration to which the TTI is attached. One such instrument is a densitometer. This instrument measures the optical density of both the active portion and the reference portion or the base portion of the xe2x80x9cbull""s eyexe2x80x9d type TTI. However, such instrumentation is expensive. Furthermore, such instrumentation is bulky and inconvenient to carry to the site of the stored rations. What is needed is a lightweight, inexpensive and simple-to-use apparatus for evaluating the color change of the active portion of a TTI label in order to determine the condition of the ration, and hence, the quality of the ration.
It is therefore an object of the present invention to provide an apparatus for evaluating the color change of an active portion of a TTI wherein the apparatus is inexpensive to manufacture.
It is another object of the present invention to provide an apparatus for evaluating the color change of an active portion of a TTI wherein the apparatus is lightweight.
It is a further object of the present invention to provide an apparatus for evaluating the color change of an active portion of a TTI wherein the apparatus is easy to use.
It is yet another object of the present invention to provide an apparatus for evaluating the color change of an active portion of a TTI wherein the apparatus can be conveniently stored when not in use.
Other objects and advantages of the present invention will be apparent to one of ordinary skill in the art in light of the ensuing description of the present invention.
The present invention is directed to a comparator for use with a time-temperature indicator that has an active portion which has an initial color and which undergoes chemical changes as time elapses. The rate of chemical change is dependent upon the temperature of the surrounding environment. The chemical changes produce visual changes in the color of the active portion of the time-temperature indicator. The comparator comprises a support member, and a plurality of comparator stages located on the support member. Each comparator stage comprises a first portion that has a reference color and a second portion that has a predetermined color that is the same as one of the colors to which the active portion of the time-temperature indicator changes as time elapses. The colors of the second portions of the comparator stages darken in a progressive manner such that the predetermined color of the second portion of a first one of the comparator stages is substantially lighter than the reference color of the first stage and the predetermined color of the second portion of a last one of the comparator stages is substantially darker than the reference color of the last comparator stage.
The number of TTI comparator stages may be varied depending on the requirements. In one embodiment, each stage is assigned indicia such as a number. For example, the initial stage can be designated by the number zero (0). Succeeding stages may be designated with consecutive positive integers. Other identification systems can also be used with the comparator stages, e.g. combinations of letters and numbers.
A user of the comparator of the present invention compares the color of the active portion of a TTI that is attached to a ration or food container (or pouch or other packaging) to the predetermined color of the second portion of each stage of the TTI comparator. The user then selects the comparator stage that has a second portion that has a predetermined color that matches the color of the active portion of the TTI label. If the shade of the color of the active portion of the TTI label is between the shades of the colors of the second portions of adjacent comparator stages, then the user selects the comparator stage that has the second portion with the lighter shade of color. The user then correlates the indicia of the selected Tm comparator stage to a particular condition of the ration.
The TTI comparator of the present invention has numerous advantages in comparison to conventional devices. For example, the TTI comparator of the present invention is relatively simple and inexpensive to manufacture in comparison to instruments such as densitometers. Furthermore, the TTI comparator of the present invention is easy to transport and may be conveniently and easily stored when not in use.